Main air vent location

Gateacre · November 19

Hello folks, I've got a bunch of mains that need venting and I'll be using B&J big mouths. I understand that it's recommended they be installed 12" before the end of main to protect them from water hammer. Several locations look basically like the photo below I'm wondering if I'd be ok doing it this way:

This I can do myself without paying someone to cut and thread in a Tee in the existing pipe. With the number of lines I have, this is significant savings. I should add that I don't have any water hammer, the boiler is operating at 1.5psi and the pipe will all be insulated.

leonz · November 19

Is this a 2 pipe system??

Gateacre · November 19

https://forum.heatinghelp.com/discussion/comment/1873143#Comment_1873143

Yes. 2 pipe all parallel flow mains.

Jamie Hall · November 19

That works,,, provided all the "horiozntal" segments can slope to drain back into the main.

Jamie Hall · November 19

ethicalpaul · November 19

I'd run it like this. You will get the appropriate pitch for free if you do it this way, and it's plenty to protect you from the commonly overstated risk (in my view) of "damage from water"

Also note that Big Mouth vents provide a LOT of venting and may be overkill. They require quite a bit of steam to get heated enough to close compared to Gorton, for example, due to their rather massive…mass.

dandub1960 · November 19

If you have no water hammer and the rads heat fine, what is it you are fixing. Two pipe systems will vent into the condensate side through the steam trap. Maybe you don't need 'em?

dandub1960 · November 19

... aside from those being the skinniest steam pipes I've ever seen.

ethicalpaul · November 19

Certainly appropriate to feed a single 2-pipe radiator however

Gateacre · November 19

Thanks Jamie, I appreciate the sanity check. I'll be sure to keep things pitched for drainage.

Gateacre · November 19

https://forum.heatinghelp.com/discussion/comment/1873176#Comment_1873176

This is the end of a 270ft main that starts as 2.5". I like your layout, it's. even easier, thanks

ethicalpaul · November 19

Yep that's a lot of main!

Gateacre · November 19

https://forum.heatinghelp.com/discussion/comment/1873182#Comment_1873182

There's no hammer but the boiler needs to run for about 3 hours to get heat to these 2 rads which are at the end of a 270' main. I've rebuild the traps with Tunstall capsules which needed to be done but slows venting even more since they don't vent as quickly as the original trap elements. This system started out burning coal and nobody thought to add mains vents when it was converted.

Gateacre · November 19

https://forum.heatinghelp.com/discussion/comment/1873194#Comment_1873194

Yup. That's the longest but there are 3 more that are each just under 200'.

mattmia2 · November 19

Are you sure this is just ordinary 2 pipe steam? Many vapor systems needed to vent the mains in to the returns through crossover traps and have the only vent to the atmosphere be at the boiler near the boiler return trap.

Gateacre · November 19

https://forum.heatinghelp.com/discussion/comment/1873218#Comment_1873218

I can't say what it was in 1910 when it was coal fired. The mains vent into the returns through appropriately sized F&T traps. The layout of the building (long but not tall with rads, in some places, on the same level as the boiler) necessitates pumped returns with vented tanks. There are some gravity returns that are vented at the boiler feed tank. No sign of a boiler return trap ever having been installed. Regardless it's 2 pipe now with regular pressuretrols, standard radiator valves and thermostatic traps etc. I'm sure it worked great when some forgotten soul would light the coals at 5am so by 8 all the air had worked its way though the traps and the system stayed under pressure until the boss went home.

dandub1960 · November 21

https://forum.heatinghelp.com/discussion/comment/1873196#Comment_1873196

Thinking on this a bit more, I wonder if those condensate returns are a bit problematic? They may have been okay to be that skinny when new, but how clear are they now. And the apparent lack of pitch makes me think they may be nearly full of water a lot of the time (and thus corrosion products).

Have you opened any of these lines and tried to blow through them (with compressed air)? I have some unpitched dry returns i suspect of constraining my venting on certain radiators.

Main air vent location

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